Method and apparatus for interfacing multiple dies with mapping for source identifier allocation

ABSTRACT

A package includes a die and at least one further die. The die has an interface configured to receive a transaction request from the further die via an interconnect and to transmit a response to the transaction request to said further die via the interconnect. The die also has mapping circuitry which is configured to allocate to the received transaction a local source identity information as source identity information, the local source identity information comprising one of a set of reusable local source identity information. This ensures the order of transactions tagged with a same original source identity and target and allows transactions tagged with different source identifiers to be processed out of order.

TECHNICAL FIELD

The present invention relates to a die, a package including a die and a further die and a method.

BACKGROUND

An ongoing trend is for the feature size in silicon technology to decrease. For example, decreasing feature sizes in CMOS (complementary metal-oxide-semiconductor) silicon processing allows digital logic to shrink in each successive fabrication technology. For example, if a digital logic cell is implemented with 90 nm (nanometer) technology, that same cell would take 55% less area if implemented with 65 nm technology.

SUMMARY

According to one aspect of the present invention, there is provided a die for use in a package comprising said die and at least one further die, said die comprising an interface configured to receive a transaction from said further die via an interconnect and for transmitting a response to said further die via said interconnect; and mapping circuitry configured to allocate to said received transaction a local source identity information as source identity information, said local source identity information comprising one of a set of reusable local source identity information.

According to another aspect of the present invention, there is provided a method comprising receiving a transaction at a die, via an interface, from a further die; allocating to said received transaction a local source identity information as source identity information, said local source identity information comprising one of a set of reusable local source identity information; and transmitting a response to said further die via said interconnect.

BRIEF DESCRIPTION OF DRAWINGS

For an understanding of some embodiments of the present invention and as to how the same may be carried into effect, reference will now be made by way of example only to the accompanying Figures in which:

FIG. 1 a shows a schematic plan view of a package incorporating two dies and circuitry to which the package is connected;

FIG. 1 b shows a schematic side view of the package incorporating two dies of FIG. 1 a;

FIG. 2 schematically shows the interface between the two die of FIG. 1;

FIG. 3 shows schematically different types of the packets transmitted from one die to the other;

FIG. 4 schematically shows two dies embodying the present invention;

FIG. 5 shows the mapper of FIG. 4 in more detail;

FIG. 6 shows the filter of FIG. 5 in more detail;

FIG. 7 shows a flow diagram of a method embodying the invention; and

FIGS. 8 a-8 h show a format of messages used in one embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In embodiments of the present invention, a plurality of integrated circuit dies is incorporated within a single package. In the following examples, a single package having two dies is described. However, it should be appreciated that this is by way of example only and more than two dies may be provided in some embodiments of the invention.

A communication channel is provided between the systems on the different silicon dies. The communications channel or on-chip interconnect may provide high bandwidth and low latency. In some embodiments, various signals are integrated onto the communication channel in order to reduce pin count and power consumption. Some embodiments of the present invention may provide a universal communication channel which allows the interface to retain their compatibility with the channel that allows for different implementations of the interfaces.

By allowing more than one die within a single package, decoupling of the analogue blocks from the digital blocks can be achieved. For example, the analogue circuitry can be provided on one die and the digital circuitry can be provided on a different die. In this way, the analogue die may have its required voltage and/or transistor gate oxide thickness whilst the digital part of the die can use a different voltage and/or transistor gate oxide thickness. It should be appreciated that in some embodiments, the digital die may predominantly contain digital circuitry and a relatively small amount of analogue circuitry and/or the analogue die may predominantly contain analogue circuitry and a relative small amount of digital circuitry.

Alternatively or additionally, each die may be designed to provide a particular function which may require various different mixes of analogue and digital circuitry in the implementation of that particular function. In some embodiments, this may mean that the same die or same design for a die may be used in different packages. By introducing this modularity, design time may be reduced.

In the following, a single package comprising two or more dies will be referred to as a system in package.

By way of example only, one system in package may comprise: a 32 nanometer die containing high speed CPUs (central processing units), one or more DDR3 controllers and other elements; and a 55 nanometer die containing analogue PHYs (physical layer devices). As the analogue circuitry is contained on a different die to that containing the digital circuitry, the 32 nanometer die is able to maximize the benefits from the reduction in size.

In the following example, a system in package embodiment is described for a set top box. In particular, in the same package are a set top box application die and a media processing engine 4. However, this is by way of example only. For example, one package could comprise an RF (radio frequency) die and a TV tuner die. Alternatively, a wireless networking PHY layer die may be incorporated in the same package as an RF die.

Alternative embodiments may be used in a wide variety of different contexts. The following is a non exhaustive list of where embodiments of the invention may be used: mobile phone chips; automotive products; telecoms products; wireless products; gaming application chips; personal computer chips; and memory chips.

Embodiments of the invention may be used where there are two or more dies in a package and the dies are manufactured in different technologies. Embodiments of the invention may alternatively or additionally be used where it is advantageous for at least one of the dies to be certified, validated or tested independently for conformance to some standard. Embodiments of the invention may alternatively or additionally be used where one of the dies contains special-purpose logic to drive specific wireless, optical or electrical interfaces so that the other die(s) can be manufactured independently and not incur any cost associated with the special purpose logic. Embodiments of the invention may alternatively or additionally be used where one of the dies contains information (for example encryption information) which is to be withheld from the designers/manufacturers of the other dies. Embodiments of the invention may alternatively or additionally be used where one of the die contains high-density RAM or ROM and it is preferable to separate this from standard high speed logic for reasons of fabrication yield and/or product flexibility.

Reference is now made to FIGS. 1 a and b which shows a system in package 12. The system in-package 12 comprises a set top box application die 2 and a media processing engine die 4. The two dies, 2 and 4, are connected to each other via an interface 6. The interface 6 comprises a bidirectional point-to-point-interface 8, a HD (high definition) video output 10 and a SD (secure digital) video output 11 from the media processing engine 4 to the set top application die 2.

The dies 2 and 4 are connected to circuitry outside the system in package. The set top box application die 2 is connected to a Wi-Fi chipset 14 and to a FLASH memory 18. The set top box application die 2 also comprises inputs/outputs 16. It should be appreciated that the number of inputs/outputs shown is by way of example only and more or less than six inputs/outputs may be provided. Each of these inputs/outputs may be both an input and an output, just an input or just an output. The set top box application die 2 is also connected to three demodulators 20 a, 20 b and 20 c. Each of the demodulators is connected to a respective tuner 22 a, 22 b and 22 c.

The media processing engine die 4 is connected to a DDR3-DRAM 24.

Reference is made to FIG. 1 b which shows the system in package of FIG. 1 a, but from the side. Again, this is a schematic representation of the system in package 12. The system in package 12 comprises PCB (printed circuit board) layers 200 with vias 202 extending there though. A substrate structure 206 is supported by balls 204 of solder, the solder balls 204 being between the PCB 200 and the substrate structure 206. The substrate structure 206 is provided with vias 208 there through. The substrate structure 206 may be of fiberglass. The substrate structure 206 has layer 0 referenced 207 d which contacts the solder balls 204. Next there is the second layer, layer 1 referenced 207 c, which is the power layer. Next there is the third layer, layer 2, referenced 207 b, which is the ground layer. Finally there is the fourth layer, layer 3, referenced 207 a, which is the signal layer which is in contact with solder balls 210.

The solder balls 210 on the side of the substrate structure opposite to that facing the PCB layers 200 support the dies 2 and 4. As is known, electrical paths are provided by the solder balls and the vias. The interface 8 is defined by paths from one die to the other die comprising: solder balls connected to the one die; the solder balls connected to the one die being connected to the signal layer of the substrate structure 206, the signal layer of the substrate structure being connected to respective solder balls associated with the other die. In some embodiments the connection path may include vias in the substrate structure. It should be appreciated that this is only one example of a possible implementation for the interface and the connections of the interface 8 may be implemented in a number of alternative ways.

The elements which are supported by the PCB layers 200 are then encapsulated in a plastic molding 212 to provide a system in package.

Some embodiments of the invention use a common interface which avoids the need for a relatively large number of wires dedicated to particular control signals. Some embodiments are such that modification of the die to take into account new or different control signals is simplified. Some embodiments of the invention are such that testing, validation and packaging of the die is simplified and the inter-die communication can be simplified.

Reference will now be made to FIGS. 2 and 3. In the following, a virtual conduit is described in which control signals such as interrupts, handshakes, reset and other narrow signals can be multiplexed with a standard memory transaction. In a typical system-on-chip (SoC) system the majority of communication is performed over a bus interconnect, via memory mapped transactions. The Bus/NoC (network-on-chip) is wide (e.g. 80 bits for NoC, 100+ bits for the bus). These narrow ‘out of band’ signals convey information on typically a small number of fixed function wires; within a SoC there may, however, be many of them. It should be appreciated that these numbers are by way of example only.

The memory mapped transactions will typically be issued from an initiator port or the like. The transactions issued from the initiator port will include an address which is used by a router to route the transactions. On the receive side, the transaction is received by a target port or the like and then routed by a router to a destination depending on the address information. The memory transactions can be considered to be routed point-to-point transactions. In contrast a control signal is point-to-point, without requiring any routing. In other words a line or wire on one die is mapped to a corresponding line or wire on the other die.

For the control signals, a signal change on a wire in one die is communicated via the interface and associated circuitry such that there is corresponding signal change on a corresponding wire in the other die in such a manner as to be functionality transparent to the entities which communicate using this wire.

Examples of control signals include, but are not limited to, interrupts, handshakes (e.g. request, acknowledge pairs), resets, power state change requests, enable/disable signals, alarm signals, synchronization signals, clock signals, status signals, functional mode setting signals, sense signals, presence detect signals, power status signals, endian signals, security mode signals, LED (light emitting diode) control, external chip control (e.g. chip select, write protect, chip enables etc) and signals taken off-chip (i.e. outside the package) to control associated electronic items.

It should be appreciated that FIGS. 2 and 3 are used to illustrate the communication between the dies 2 and 4 of FIG. 1.

In some embodiments of the present invention, the majority of the communication between the two dies 2 and 4 connected by the inter-die interface 8 will be read and write transactions to the memory address space associated with the respective dies. This traffic will generally be two-way traffic. However, there may also be communication in the form of the assertion and/or de-assertion of interrupt lines, DMA (direct memory access) handshakes, reset requests and acknowledgments, power down requests, and/or the like. These signals can additionally or alternatively include any one or more of the controls signals mentioned above. These latter signals are the control signals discussed previously and are sometimes referred to out of band signals (OOB).

In one embodiment of the present invention, the memory transactions (for example read and write) are carried by a sequence of packets over the inter-die interface 8. In this regard, reference is made to FIG. 2 which shows the inter-die interface.

A packet multiplexer 26 is provided on each of the dies. This is connected to the inter-die interface 8, at the other end of which is a respective packet de-multiplexer 28. Each die thus comprises a packet multiplexer for the traffic going to the other die and a packet de-multiplexer for the traffic received from the other die. For simplicity, only one packet multiplexer and de-multiplexer is shown. As can be seen, the packet multiplexer receives an input from a respective bundle 30 ₀-30 _(N). In the example shown, there are N+1 bundles each of which has b wires. In this example, each bundle has the same number of wires. However in alternative embodiments of the invention, each bundle may have different numbers of wires. Each wire is connected to a respective register 31 _(0-n) which holds the current signal value associated with that wire.

Each wire is allocated a predefined position within one bundle. One or more respective signals are associated with a particular wire. Thus a particular signal will be allocated a particular wire in a particular bundle of wires. For example, the power down request will be allocated wire number b+1 in bundle 1. Each bundle is arranged to be transmitted as a single packet together with a bundle identifier which is referred to as a virtual channel identifier.

The packet may be atomic.

The packet multiplexer 26 receives an input in the form of packets from one or more of the bundles. The packet multiplexer also receives memory transactions which have been split into packets. The packet multiplexer multiplexes the packets output by the bundles and the memory transaction packets and transmits them across the point-to-point interface 6 to the packet de-multiplexer 28.

The packet de-multiplexer 28 uses the bundle identifier of the bundle packets to direct each received bundle packet to a respective incoming bundle circuitry 32 ₀ to 32 _(n). There is a respective bundle circuitry 32 associated with each bundle from the transmit side. The respective incoming bundle circuitry 32 associate each bit in the received packet with the associated output wire and output the associated value to the associated incoming bundle registers 33. In FIG. 2, the bundle registers 33 are shown as a single block for simplicity. In practice a register is associated with each wire.

There may be one-to-one mapping. For example, if wire 1 on bundle 0 has a particular signal value on the transmit side, the output 1 of the register for bundle 0 will have that signal value. In alternative embodiments, there may be a more complicated mapping between the input on a particular wire of a particular wire and the output of the register. For example there may not be one to one correspondence between wires of a particular bundle and a given register. The wires of one bundle may correspond to respective outputs of different registers.

In one embodiment two or more wires may map to a fewer number of wires. Alternatively one or more wires may map to a greater number of wires.

In one embodiment of the invention, the state of each wire in the bundle is not continuously transmitted. The state of the wire is sampled at regular intervals and these samples are transmitted across the interface 8 in a respective wire packet along with data traffic. The sample may be used to specify the state of the respective register 31 which holds the state of each out of band signal on the transmit side of the interface. In the embodiment shown, there are n+1 registers 31 _(0-n).

The number of registers may be the same as the number of wires or less than the number of wires. In one embodiment, each register is connected to a single wire. Alternatively or additionally, one register may be connected to two or more wires. Where a register connected to more than one wire a plurality of bits may be used to represent information such as a state or the like.

In one embodiment, the transmission in the interface 8 is performed bi-directionally so that the wires can be virtually connected from either side. As mentioned each die has a packet multiplexer and a packet de-multiplexer. The packet multiplexer and de-multiplexer may share the same physical interface so that a die will receive and transmit via a common interface, that is on the same physical connection. Alternatively, a packet multiplexer and de-multiplexer on one die have separate interfaces. In other words, a die will receive and transmit on different interfaces.

The interface can be regarded as a set of wires or connectors extending between the two dies. The wires may be subdivided into one or more lanes. Where the wires are subdivided into lanes, the or each lane may be arranged to carry packets.

It should be appreciated that in embodiments of the invention, the same connectors or wires which carry the memory transaction packets also carry the bundle packets. The interface 8 may be considered in some sense universal and is capable of carrying different classes of communication such as signals (control signals) and busses (memory transactions).

The interface 8 can be implemented in serial or parallel form. The data in a packet may be transmitted serially or in parallel. It is preferred that the interface 8 be a high speed link.

In a preferred embodiment of the present invention, the sampling rate, the number of bundles transmitted and/or the priority of transmission of these bundles can be configured as required.

In one embodiment, the states of signals comprising each wire bundle can be periodically sampled at a rate which is separately configurable for each bundle. In other words, each bundle can have a different sampling rate associated therewith.

Each bundle sample is formatted into a packet as illustrated in FIG. 3. The bundle sample may be formatted in the respective bundle 30 where the additional information to packetize the bundles samples are added. In an alternative embodiment, the multiplexer may incorporate circuitry which is configured to perform or complete the packetization.

The bundle sample packet is referenced 34. The first field 36 a of the bundle sample packet 34 comprises information to identify the packet to the receiving logic as a wire bundle packet. In this example, this field of the packet comprises two bits. However, it should be appreciated that in alternative embodiments of the invention, more or less than two bits may be used for this field. This field is followed by a bundle identity field 36 b. The bundle identity field allows the packet to be routed to the appropriate bundle circuitry 32 on the receiving die. This therefore identifies the bundle from which the packet originates. In this example, the field comprises 8 bits. However, it should be appreciated that more or less than 8 bits may be used. The packet payload 36 c comprises b bits, one for each input wire to the bundle on the transmitting side.

By way of example only, b may be, for example 80 bits. In one implementation, there may be four bundles. The appropriate payload is routed to the appropriate bundle circuitry 32 on the receive side, shown in FIG. 2 using the bundle identification. The bundle circuitry 32 will map the bundle payload to the appropriate incoming bundle register 33.

It should be appreciated that the sizes of the respective fields of the packet may be changed in different embodiments of the invention. It should be appreciated that the order of the fields may also be changed in different embodiments of the invention.

In one embodiment of the present invention, each bundle is sampled at a rate of (CLK)/2^(N) where CLK is the clock rate and N is one of: (2, 3, 4 . . . 31). For example, a clock CLK of 400 MHz and a bundle configured with N=8 would sample that bundle at 1.56 MHz and would produce a wire packet for that bundle every 640 nanoseconds.

In one embodiment of the present invention, at any given time there may be none, one or more than one packet ready for transmission. The packet multiplexer 26 illustrated in FIG. 2 will comprise logic to arbitrate, if necessary, and decide on the transmission order of the packets. This will typically produce a time division multiplexed of bundle packets and memory packets on the physical transmission on the interface between the first and second die.

As mentioned previously, the interface 8 is also used for the memory transactions such as memory reads and/or writes. An example of the memory transaction packet 38 which is sent across the same interface 8 is also shown in FIG. 3 and is referenced 38. The first field indicates that the packet is a NoC (network-on-chip) packet. The second field 40 b indicates the FIFO-ID (first-in first-out identifier). As shown in FIG. 2, the die comprises queues implemented by FIFOs. In the embodiment shown in FIG. 2, there are two FIFOs which provide a high priority queue 35 and a low priority queue 37. The interconnect delivers the memory transaction to the appropriate FIFO depending on which queue the transaction belongs to. There can be more than two queue classifications in alternative embodiments. The third field 40 c indicates if the packet is a head packet, a tail packet or an intermediate packet. One memory instruction may be sent in a plurality of different packets.

The final field is the payload field 40 d which includes the address and/or data to be written or read and/or the associated instruction and/or the transaction attributes of belonging to the protocol used on chip to perform memory transactions. The NoC field is allocated 2 bits, the FIFO-ID field is allocated 6 bits, information as to whether the packet is a head, a tail or intermediate packet is allocated 2 bits and the payload is allocated B bits. It should be appreciated that the actual sizes of the respective field is by way of example only and alternative embodiments may have different sizes for the fields.

As can be seen, the wire packet 34 and the NoC 38 packet have the same format as represented by the general packet format 42. The first 2 bits 44 a represent the type of the packet. The second 6 bits represents the VC-ID 44 b (virtual channel-identity). This is followed by the segment identifier 44 c and the payload 44 d. The type is allocated 2 bits, the VC-ID 44 b is allocated 6 bits, the packet ID segment ID 44 c is allocated 2 bits and the payload 44 d is allocated B bits.

In one modification, a time slot structure may be used where packets are allocated to a particular time slot. This may be controlled by the packet multiplexer or control circuitry associated therewith. Time slots could be assigned to particular wire bundle packets or to memory transaction packets belonging to a particular priority queue.

In embodiments of the present invention, the packets may be sent serially or in parallel. One embodiment of the present invention involves transmitting the packets in a narrow parallel form with, for example, seven or fifteen wires.

The packets, when received are latched into the bundle circuitry 32 on the receiving side. Once latched, the incoming bundle circuitry 32 causes the values to be stored to the appropriate register 33. The signals can then be asserted to where the incoming signals need to be mapped on the incoming die. For example, interrupts will typically be mapped directly to the interrupt controller of the main CPU.

The packet/bundle mapping is performed in a simple one to one manner without permutation, in one embodiment of the invention. This means that wire W of bundle B on the outgoing bundle is mapped to wire W of bundle B on the incoming bundle circuitry 32 for all implemented values of W and B.

Embodiments of the present invention may permit an initiator of a transaction to work in a global out of order local order (GOOLO) context. This means that the system ensures that the order of transactions tagged with the same source identifier value and allows transactions tagged with different source identifiers to be processed out of order. In particular, if there is an outstanding transaction with a particular source identifier and a particular target, when a further transaction is received, that further transaction will be blocked if the further transaction has the same source identifier as the outstanding transaction but a different target.

By way of example only, embodiments could be used in a context with multiple processors working in parallel with multiple targets. One example is an AXI protocol based ARM core provided by ARM Limited. For example, this provides a capability to work in parallel on multiple targets using multiple source identifiers in order to optimise the CPU performances. It should be appreciated that this is by way of example only and embodiments of the invention can be used with many other different cores and/or functions.

Reference is made to FIG. 4. In FIG. 4, there is a first die 2 and a second die 4 which are connected one to the other by an interconnect 106. The first die 2 comprises a transaction initiator 100. The initiator 100 of the transaction on the first die 2 is seeking a response from circuitry 114 on the second die 4. In this example, the circuitry 114 is memory circuitry.

It should be appreciated that in this example, the first die 2 comprises the initiator 100 of the transaction while the second die 4 comprises the recipient 114 of the transaction and generates a response which is sent back to the initiator 100 on the first die 2. In practice, each die will be both an initiator and a responder so that the circuitry shown schematically in relation to die 4 will also be present in die 2 and the circuitry shown schematically in die 2 will also be present in die 4.

The initiator 100 is arranged to put the generated transaction onto the bus 102 of the first die. The bus 102 connects the initiator 100 to interface circuitry 104. The interface circuitry 104 is coupled to the interconnect 106. The interconnect 106 is provided between the first die 2 and the second die 4.

The second die 4 comprises an interface 108 which is connected on the one hand to the interconnect 106 and on the other hand to a mapper 110 via bus circuitry 114. The mapper 110 is connected by bus circuitry 116 to memory circuitry 114. It should be appreciated that the bus circuitry 115 between the interface 108 and the mapper 110 and the bus circuitry 116 between the mapper 110 and the memory circuitry 114 may be provided by common bus circuitry.

Each die may act as an initiator or a responder or both. In the figures, each die is shown as having a single interface. In alternative embodiments, each die may have more than one interface. For example, separate interfaces may be provided on one or other of the dies dependent on whether the die is acting as an initiator or a responder or both. Likewise, the interconnect between the dies may be shared by the initiation and response traffic provided to and from a die. Alternatively, the initiator traffic from one die may use one interconnect and a separate interconnect may be provided for the response traffic to that one die.

The initiator 100 may be a processor or the like. The initiator 100 is configured to initiate a transaction which requires a response. The transaction can be any suitable transaction and may be for example a memory transaction. The transaction may for example be read request or a write request.

The packet which is received by the interface 100 of the second die 4, via the interconnect 106 will comprise an address field which identifies the target of the transaction on the second die 4, a source identity field which identifies the source of the transaction on the first die and a size field which indicates the size of the message. The format of the messages will be described in more detail later.

Reference is made to FIG. 5 which shows the mapper 110 in more detail. The mapper 110 comprises a filter 154, an address decoder 150, a source identity circuitry 152 and a buffer 156. The buffer provides a retiming function and may be omitted in some embodiments. In other embodiments the buffer may be part of the bus circuitry. The filter 154 and address decoder may be operating in parallel so that the time taken to process the transaction in the mapper is minimized. The mapper 110 is connected to the interface 108 and the bus circuitry 116.

The transaction from the initiator 100 comprises a request part 158, a source identity part 166 and a target address part 160. The request part identifies the nature of the transaction, for example that the transaction is a read transaction. The source identity information part identifies the identity of the initiator 100 on the first die. The address part indicates the address at which the transaction is targeted, for example the memory address to be read. These parts may be provided by one or more respective fields.

The request part 158 from the initiator 100 is passed from the interface 108 to the mapper 110 and in particular is input to both the address decoder 150 and the filter 154. The address decoder 150 is also arranged to receive the target address part 160 from the interface 108. The address decoder 150 is arranged to process the address to provide a decoded address 164 to the filter 154.

The source identity circuitry 152 is arranged to receive the source identity part 166 from the initiator. The source identity circuitry takes the source identity of the original initiator and puts this information into a different information field 174 and sends this information to buffer 152. The source identity circuitry 152 is also arranged to receive the response data part 168 of the response to the transaction, from the bus 116. The source identity circuitry 152 also receives buffered source identity information included in the different information field. This input is referenced 178. In this way, the source identity circuitry 168 is configured to provide the original source identity (which was in the different information field) as a source identity for the response part 172, which is output to the interface 108. The source identity response part 172 has the source identity associated with the response data part 168 received from the bus.

The filter 154 is shown in more detail in FIG. 6 and will be described with reference thereto.

As already mentioned, the filter receives the request part 158 and the source identity part 166 of the initiator request. The filter also receives the target signal (decoded address) 164 from the address decoder.

Reference is made to FIG. 6 which shows the filter in more detail. The filter has a depth of “n+1”. This represents the maximum number of different source identifiers for outstanding transactions. Each different source identifier can be associates with a single target only. The depth is thus the maximum number of entries which can be supported by the filter. Each of those different source identifiers may have one or more outstanding transactions. However, the source identifier can only have outstanding transactions with one target at a time. Accordingly, when the filter receives a request part 158, the source identity part 166 and the target signal, it checks the initiator source identity information and the target information.

If one of the entries is already associated with the same source identity and target, then the new request is associated with that same entry and a counter associated with that entry is incremented by 1.

If, on the other hand, the filter determines that the received source identity information and the received target information are not associated currently with any of the entries, then an available entry is assigned to that source identity information and target information. This may be the next available entry or may be allocated in any other suitable way. The counter of that entry will be incremented from 0 to 1. The source identity information and the target information will be stored in respective fields of that entry.

If the filter determines that the received source identity information is associated with one of the entries but that the target is not same target in that entry, then that transaction is blocked. In other words, the transaction associated with a source identity which has an outstanding transaction with a different target is blocked and not propagated to the different target.

A local source identity value is associated with each entry. For example, SRCn=n for the entry n. This is the source identity value used by the bus 116 of the second die 4 to manage the response request routing back to the mapper and the routing from the mapper to the target. It should be appreciated that there set of local source identity values are reusable. If at time t, a source identifier and target are give local source identity a, at time t+x later, that same source identifier and same target may be allocated a different local source identity. The set is thus completely reusable and allocation of the local source identity is based on availability, regardless of the original first die source identity.

Schematically, the filter is shown as having a multiplexor 180 which is connected to each of the entries. The multiplexor has a control signal 182 which allows one of the local source identity values 184 to be output to the buffer 156. The filter 154 also outputs the request part 188. If the request part is to be propagated, then the original request is output. If the request part is to be blocked, then the request part with have instead or additionally indicates that the request is not to be routed to the target. For example a bit may be added. If the request is to be propagated to the target, the bit will have one value and if the bit is not to be propagated, then the bit will have the other value.

A grant signal will be received from the buffer 156, in response to the buffer receiving and granting or denying the request. The request is granted or denied in dependence on the information provided by the filter as to whether or not the request is to be propagated to the target. This grant signal is provided to the address decoder 150, the filter 154 and the interface 108.

The filter 154 also receives from the bus 116 the response data part 168 and the source identity for the response part 176 from the bus. The source identity included in the source identity for the response part will be the source identity locally allocated by the filter 154. When the response is received with a particular local source identity, the entry associated with the local source identity is identified and the counter of the identified entry is decremented. For example, if the response is received for the local source identity of n, the counter for entry n is decremented by 1. When the counter has been decremented to 0, then that entry is then available for allocation again. Any suitable scheme for determining a number of outstanding transaction for a given source and target may be used alternatively or additionally to the counter.

The buffer 156 thus receives the request part from the filter 188 and the local source identity 184 from the filter 154. The buffer receives the original source identity information 174 in the different information field from the source identity circuitry 152.

The buffer 156 is arranged to output the modified transaction comprising a request part 192 (as received from the filter 154), a local source identity information part 198 (as received from the filter 154) and the original source identity information in the different field (as received from the source identity circuitry 152) onto the bus 116. When the modified transaction is accepted onto the bus, grant signal 194 is received by the buffer. In practice, there will be an arbitrator arranged to arbitrate between the various requests for access to the bus.

The response output by the mapper 110 to the transaction comprises the original source identity part 172 as output by the source identity circuitry 152, and the response data part 168 from the bus 116, which is also input to the filter 154.

Reference will now be made to FIG. 8 which shows the message structure used in one embodiment of the invention. The message which is provided by the initiator 100 can be seen from FIG. 8 a. It should be appreciated that the transactions discussed are by way of example only and the transaction may be any transaction where an initiator requires a response from a target on a second die. The response may be a simple acknowledgement or grant, or may additionally or alternatively require some data.

The message may be in the form of a packet or may take any other suitable format. The message comprises a first field 120. This first field 120 comprises the memory address which is to be read. This is the target address (and is referred to as signal 160 in FIG. 5). This address field will identify a unique location on the second die. The address information will thus be sufficient to ensure that the packet is routed to the second die and that the appropriate memory location on the second die will read. This field or an additional field will comprise an opcode or the like defining the nature of the transaction, e.g. is the transaction is a read request, a write instruction or the like. This latter information comprises the signal 158 of FIG. 5.

The second field 122 defines the size of the packet. The third field 124 has the source identifier 124 of the initiator 100. For example the initiator 100 may have for example have n source identifiers associated therewith. One of the n source identifiers is used. Typically the source identifiers will be from the set of: 0, 1 . . . n−1. n can have an integer value of 1 or more.

The interconnect 102 is arranged to modify the packet of FIG. 8 a and this is shown in FIG. 8 b. The first field is the address field 120, as in FIG. 8 a. Likewise, the second field 122 is the size field, again as in FIG. 8 a. The third field 126 includes a modified version of the source address 100 (this is the signal referenced 166). Typically a die will have more than one initiator. For example a first initiator may use a range of source identifiers of 0 to n−1 and a second initiator may use a range of source identifiers of 0 to m−1. In one embodiment, the interconnect 102 adds no offset to the source identifiers from the first initiator and an offset of n to the source identifiers of the second initiator. In this way the source of each transaction is uniquely identified. The modified version of the address means that the initiator is identified as well as the particular source address of that initiator. Thus the offset added to the source address is dependent on which initiator is providing the transaction. In this way the identity provided in field 126 will uniquely identify the initiator and the source address within the initiator.

The packet shown in FIG. 8 b is put by the interface 104 onto the interconnect 106.

The packet shown in FIG. 8 b is therefore received by the interface 108 of the second die 4. The mapper 110 is arranged to modify the packet as shown in FIG. 8 c. The first field is the address field 120 as discussed for example in relation to FIG. 8 a. The second field shown is the size field 122 which is similar to the size field shown in FIGS. 8 a and 8 b. However it should be appreciated that the value in this field may be altered if the size of the packet has been altered.

The third field 128 represents a new source identifier which is assigned by the mapper 110 as discussed previously. This new source identifier value is used on the second die to ensure that the response is routed back to the mapper 110 In the fourth field 130, the source identifier from the first die is included in the new user defined field of the interconnect transaction. This field comprises the first die source identity and includes the information which was included in the third field 126 shown in FIG. 8 b. This is to allow the response to be routed back to the first die.

The packet shown in FIG. 8 c is put onto the bus 116 of the second die 4.

The interconnect bus 116 will modify the packet. The modified packet is shown in FIG. 8 d. The first field, the second field and the fourth field are as shown in FIG. 8 c. However, the third field is modified to include a modified version of the local source identifier. In a similar manner to that described in relation to FIG. 8 b and for the same reasons, an offset is added so that the modified local source identifier for the second die is provided. This offset will allow the mapper to be uniquely identified from other sources on the second die. The mapper could be regarded as being or at least analogous to an initiator in this regard.

Using the address information included in the packet, the bus 116 will ensure that the memory transaction is routed to the memory circuitry 114. The memory circuitry 114 will ensure that the requested information is, for example read out. The packet provided by memory circuitry 114 is put onto the bus 116 is shown in FIG. 8 e. The packet will comprise a first field 134 which comprises the requested data. The second field 132 comprises the modified local source identifier, as shown in the third field of FIG. 8 d. The third field contains the same information as the fourth field of the packet as shown in FIG. 8 d. Using the modified local source identifier, the response can be directed to the mapper.

The interconnect bus 116 is arranged to modify the packet put by the memory circuitry 114 onto the bus to the format shown in FIG. 8 f. The first and third fields are the same as shown in FIG. 8 e. The second field is modified to insert instead the local source identifier for the second die, as discussed in relation of third field of FIG. 8 c, in other words to remove the offset. The local source identifier is used to route the response to a particular address of the mapper.

The mapper 110 receives the packet shown in FIG. 8 f and provides the packet as shown in FIG. 8 g. This response packet consists of a first field with the requested data 134 and a second field which includes the original first die source identity, that identity being the identity as discussed in relation to the third field of the packet of FIG. 8 b. That packet is transmitted across interconnect 106.

The packet is received by the interface 104 of the first die which causes the packet to be modified to the format shown in FIG. 8 h. In particular, the first field comprises the requested data 134 and the second field comprises the local source identifier 124 as discussed in relation to the third field of FIG. 8 a. The offset is thus removed. This response is then routed to the particular address of the initiator 100 which sent the original request.

Thus, the source identifier used in the first die is not treated as a source identifier in the second die and vice versa. The first die identifier is carried in the packet in the second die inside a user defined field of the interconnect transaction, this being the field containing information 130. This information is used to allow the response to be routed back to the first die. In the second die, a new source identifier is assigned to the inter-die request i.e. the request from the first die as discussed previously. This mapping is reversed for those response transactions leaving the second die and going back to the first die. The source identifier assigned by the mapper 110 is used to ensure the response is routed back to the mapper. The mapper 110 is also arranged to re-assign the original source identifier carried inside the packet to the response transaction before the response transaction leaves the second die. The original source identifier value of the first die is then used for local routing in the first die of the response transactions which are returned from the second die.

Reference is now made to FIG. 7 which shows a method embodying the present invention.

In step S1, the transaction request is received at the second die.

In step S2, the original source identity information is put into a different field.

In step S3, a determination is made as to whether or not there is already at least one outstanding transaction with the same source identifier. If there is already at least one outstanding transaction, with the same source identifier, the next step is step S4 a and it is determined if the target is the same. If the target is the same, the next step is step S4 b. The counter is incremented by 1 and the local source identity information allocated to previous outstanding transactions having the same source identity information and target is used. If the target is not the same, the next step is step S4 c and the transaction is blocked.

If there is not already at least one outstanding transaction with the same source and target, then the next step is step S5. An allocated entry is allocated to the source identity information and target information and the local source identity information associated with that entry is used. The counter is also incremented by 1.

It should be appreciated that steps S3, S4 and S5 can take place before, after or generally at the same time as step S2.

The next step is step S6 which takes place generally after steps S4 b or S5 and step S2. In this step, the request is routed to the target with the local source identity information as the source identity information and the original source identity information in a different field.

In step S7, the response is received from the target.

In step S8, the counter associated with that transaction for which the response has been received is decremented by 1. If the counter value is 0, then the local source information becomes available for allocation to a different source and target pair.

In step S9, the local source identity information is replaced with the original source identity information.

In step S10, the response is sent back to the initiator. It should be appreciated that step S8 can take place before, after or generally at the same time as steps S9 and S10.

It should be appreciated that the orientation of the respective dies with respect to the substrates can be changed as compared to the flip chip orientation shown in FIG. 1 b.

In alternative embodiments of the invention, the dies may be arranged in a stacked arrangement, one above the other.

The interface between the two dies is described in preferred embodiments of the invention as being a wired interface, that is provided by a series of wired or wire patterned connections. In alternative embodiments of the invention, the interface may be provided by any suitable means for example an optical interface or a wireless interface.

For clarity a number of the embodiments described show one of the dies as transmitting to the other die which receives the signals. It should be appreciated that in some embodiments of the invention both dies may have the “transmitting” part of the circuitry and the “receiving” part of the circuitry so that the interface is bi-directional. It should be appreciated that in some embodiments at least some of the wires or other interface mechanism are bidirectional. In alternative embodiments the interface may comprise two separate paths, on path for received packets and the other path for transmitted packets.

It should be appreciate there may be more than two dies in some embodiments of the invention. 

1. Apparatus comprising a die for use in a package comprising said die and at least one further die, said die comprising: an interface configured to receive a transaction from said further die via an interconnect and for transmitting a response to said further die via said interconnect; and mapping circuitry configured to determine that at least one outstanding transaction with a same original source identifier as said received transaction, and in response to that determination allocate to said received transaction a local source identity information as source identity information that is the same as previously allocated to said at least one outstanding transaction, wherein said allocated local source identity information comprises one of a set of reusable local source identity information.
 2. The apparatus as in claim 1, wherein said mapping circuitry is configured to allocate to said received transaction the same local source identity information as previously allocated to said at least one outstanding transaction if it is determined that the at least one outstanding transaction has both a same original source identifier and a same target information as said received transaction.
 3. The apparatus as in claim 1, wherein said mapping circuitry is configured to prevent propagation of the received transaction if the received transaction has a same original source identifier information as said at least one outstanding transaction and different target information as the at least one outstanding transaction.
 4. The apparatus as in claim 1, wherein said mapping circuitry comprises a counter associated with each of said reusable local source information, said counter associated with said allocated local source information being adjusted in response to said transaction being allocated said allocated local source information.
 5. The apparatus as in claim 4, wherein said counter associated with said allocated local source information is oppositely adjusted when a response to said transaction is received.
 6. The apparatus as in claim 5, wherein said counter associated with said allocated local source information reaches a predetermined value indicative of no outstanding transactions, said allocated local source information is reusable by received transactions having a different original source identity information.
 7. The apparatus as in claim 1, wherein said mapping circuitry is configured to modify said received transaction to provide original source identity information in said received transaction in a further field.
 8. The apparatus as in claim 7, wherein said mapping circuitry is configured to receive a response to said transaction and to modify said response to provide the original source identity information in a source identity information field of said response.
 9. The apparatus as in claim 1, comprising routing circuitry configured to route a response to said transaction in said die using said local source identity information.
 10. The apparatus as in claim 1, wherein the die further includes a memory and said transaction comprises a memory access transaction.
 11. The apparatus as in claim 1 further comprising a package comprising the die and said further die.
 12. A method comprising: receiving a transaction at a die, via an interface, from a further die; determining, with filter circuitry, that at least one outstanding transaction with a same original source identifier as said received transaction; allocating, with mapping circuitry, to said received transaction a local source identity information as source identity information that is the same as previously allocated to said at least one outstanding transaction, wherein said allocated local source identity information comprises one of a set of reusable local source identity information; and transmitting, via said interface, a response to said further die.
 13. The method as in claim 12, wherein allocating comprises allocating to said received transaction the same local source identity information as previously allocated to said at least one outstanding transaction if it is determined that the at least one outstanding transaction has both a same original source identifier information and a same target information as said received transaction.
 14. The apparatus as in claim 12, further comprising preventing propagation of the received transaction if the received transaction has a same original source identifier information as said at least one outstanding transaction and different target information as the at least one outstanding transaction.
 15. Apparatus comprising a die for use in a package comprising said die and at least one further die, said die comprising: a memory; an interface configured to receive a memory access transaction request from said further die via an interconnect and to transmit a memory access transaction response to said memory access transaction to said further die via said interconnect; and mapping circuitry configured to receive the memory access transaction request which includes first source identity information, said first source identity information associated with a source of said memory access transaction request in said further die, determine that at least one outstanding memory access transaction with a same first source identity information, and in response to that determination allocate to said received memory access transaction a second source identity information that is the same as previously allocated to said at least one outstanding memory access transaction, wherein the second source identity information comprises one of a set of reusable second source identity information values associated with the mapping circuitry.
 16. The apparatus as in claim 15, wherein said mapping circuitry is configured to prevent propagation of the received memory access transaction request to the memory if the received memory access transaction request has a same first source identity information as the outstanding received memory access transaction request but has a different target information than that outstanding received memory access transaction request.
 17. The apparatus as in claim 15, wherein said mapping circuitry comprises a counter associated with each of said second source identity information values, said counter indicative of outstanding received memory access transaction requests using said second source identity information value, and operable to control allocation of said second source identity information value to subsequently received memory access transaction requests with different first source identity information until all outstanding received memory access transaction requests have been serviced. 